Field
The present invention relates to a light emitting module, and more particularly, to a light emitting module including a lens for use as a surface illumination or a backlight of a liquid crystal display.
Discussion of the Background
There are edge-type backlights and direct-type backlights for backlighting a liquid crystal display. As for the edge-type backlights, light emitting diodes (LEDs) are arranged on a side of a light guide plate, and light incident from a light source backlights a liquid crystal panel by using the light guide plate. The edge-type backlights can reduce the number of LEDs and does not require a high level of quality deviation among LEDs. Therefore, the edge-type backlights are cost-effective and are advantageous to development of low power consuming products. However, the edge-type backlights can hardly overcome a difference in contrast between an edge portion and a central portion of the liquid crystal display, and has a limitation in implementing high picture quality.
On the other hand, as for the direct-type backlights, a plurality of LEDs are arranged directly under a liquid crystal panel at constant intervals, and light from the LEDs backlights the liquid crystal panel. The direct-type backlights have advantages that can overcome a difference in contrast between an edge portion and a central portion of the liquid crystal panel and can implement high picture quality.
However, in the case of the direct-type backlights, if the respective LEDs cannot uniformly backlight a relatively large area, it is necessary to densely arrange a larger number of LEDs, resulting in an increase in power consumption. In addition, if the LEDs have quality deviation, the liquid crystal panel is non-uniformly backlighted, making it difficult to secure uniform quality of a screen.
In order to reduce the number of LEDs used, technique for dispersing light by arranging a lens in each LED may be used. However, even a slight change in alignment between the LED and the lens may cause a serious change in distribution of light emitted through the lens, making it more difficult to uniformly backlight the liquid crystal panel.
Also, as illustrated in FIG. 1, when a lens having a disk-shaped light orientation pattern LP is applied, a bright portion WP in which adjacent light beams cross each other and a dark portion BP in which light is rarely irradiated may be formed.
The bright portion WP can be controlled by reducing luminous flux travelling toward the bright portion WP, while adjusting brightness based on an viewing angle of the light orientation pattern LP. On the other hand, the dark portion BP can be controlled by increasing the size of the light orientation pattern LP or reducing a gap between the LEDs. However, if the luminous flux travelling toward the bright portion WP is reduced so as to remove the bright portion WP, the dark portion BP may further darken, and conversely, if the size of the light orientation pattern LP is increased or the gap between the LEDs is reduced so as to remove the dark portion BP, the bright portion WP becomes wider and brighter. In other words, it is difficult to remove both the bright portion WP and the dark portion BP.